Herring spawn on display in bay

Updated 11:12 pm, Sunday, January 13, 2013

You might have seen it late last week: the event that has transformed San Francisco Bay.

Just off San Francisco's China Basin, you could see flocks of gulls and pelicans flying, hovering and then crashing into the bay to feed. The big pelicans hit the water with such force that it looked like somebody was dropping bowling balls from a helicopter.

A big herring spawn was taking place.

The migratory baitfish enter San Francisco Bay in winter to spawn. Marine birds, sturgeon, and other birds and fish come from near and far to gorge on the eggs and the herring themselves.

So do commercial fishermen, to net the herring to cash in on a short-term lucrative catch. As a commercial fishery, it is one of the most regulated in the industry.

The arrival of the herring early last week had a profound effect on the bay system. In the North Bay, where sturgeon fishing appeared on the verge of breaking loose for the season, it seemed like the sturgeon vanished overnight. That's because they did.

The consensus is that large numbers of sturgeon from throughout the bay's system somehow knew that the herring had arrived in the central bay and headed straight for the vicinity of China Basin to feed. When herring spawn, sturgeon love nothing more than feeding on the eggs.

So much, in fact, that a large area of the central bay is closed to fishing through March 15 because sturgeon can crowd together to feed on herring eggs and become vulnerable to poachers who illegally snag them.

Most herring are just 5 to 8 inches long, yet the females deposit about 30,000 eggs in a single spawn. The clusters of eggs adhere to crevices in rocks and any structure, such as docks and seaweed, then hatch 40 days later. As the herring grow into adulthood, they roam the ocean in vast schools and provide a link in the marine food chain. Humpback whales, orcas, dolphins, salmon, striped bass and scores of seabirds are among those that follow and prey on the big schools of herring.

When you see a herring spawn in the bay, you are seeing a glimpse of nature's way that dates back thousands of years.

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